Also, on page 5, the Professor's desk has objects that look exactly like Moneko, the proxy for the eldest vampire sister (Azami). It makes me wonder if the two are the same person: the Professor says that their body and the laboratory are one and the same; Moneko being able to drink tea despite being a proxy might be related to this.
Oh, good point. Also, Moneko has those perpetually closed eyes like the Professor. She might legit be Azami. If that is the case, and if possibly my theory is correct, then it's was the four sisters, Dahlia, Rubeckia, Arctotis and Usyuki that were involved in the possible coup against their mother. Azami, Yomogi and Shion didn't have anything to do with it. The two eldest sisters are maybe more neutral, but Shion is out for revenge. I mean, it could just be one big power struggle between the sister and none of them had a hand in their mother's death, but I think I'll stick to my theory until it gets disproven.
Another possibly stupid theory I have is about the Ice Cream Man. I think the revelation might be that he's the vampire girls' human father. I really have no evidence for this, it's really just something I thought might be the case. I'm most certainly wrong about this. When he was referring to Shion, he just called her "the youngest" implying some familiarity with the sisters. Also his description in the end, about how he's a mysterious man, he cares about kids, and that his mind isn't sound, which might be due to being infected with the formula. All of these feel like subtle clues hinting that he might indeed be the dad. And if the Professor really is Azami, she might also be searching for a way to cure the infection too in order to save her dad. Again, this is just me making wild theories out of basically nothing, most likely it's all wrong.